The present invention relates to the preparation of a poly(2-hydroxyethyl methacrylate) polymer (hereinafter PHEMA) and more particularly to a new precipitation/suspension polymerization process for its preparation.
PHEMA and related acrylic polymers have been prepared by suspension polymerization and solution polymerization techniques. These polymers are typified by being organic solvent soluble and water insoluble. Such hydrophylic polymers are capable of generating a water-insoluble hydrogel. PHEMA in particular has exhibited special utility as a basis for preparation of a synthetic bandage or dressing which can be applied to burns and other wounds as proposed in U.S. Pats. Nos. 3,963,685 and 4,563,184.
Prior suspension polymerization proposals include U.S. Pat. No. 3,583,957 which shows the polymerization of PHEMA containing appreciable di-acrylate cross-linker (ethyleneglycol dimethacrylate) in an aromatic hydrocarbon solvent under conditions which exclude stirring to produce PHEMA polymer particles of less than about 10 microns in particle size. U.S. Pat. No. 4,076,921 (and corresponding UK Pat. No. 1,403,387) propose a similar no-stirring process to produce about 1 micron sized particles wherein the cross-linker level ranges from about 0.02 to about 0.2% by volume of the entire reaction mixture. Solvents include aromatic hydrocarbons, hydroaromatic hydrocarbons, halogenated derivatives of aliphatic or cycloaliphatic hydrocarbons, esters of carbonic acids and aliphatic alcohols, ethers and cycloethers, and ketones and cycloketones. U.S. Pat. No. 3,998,305 proposes yet another similar process of producing about one micron sized PHEMA polymer particles wherein the criticality of cross-linker is stated to be less than 0.2 vol-% by weight of the reaction mixture. U.S. Pat. No. 4,696,974 proposes yet another nostirring process utilizing toluene solvent wherein the crosslinker level ranges from about 1 to 3 percent by weight of the HEMA monomer fed to the process.
It should be noted that solution polymerization techniques also have been proposed in the art for production of HEMA polymer particles. Regardless of the technique employed in preparing the PHEMA polymer particles, the art describes the formation of wound dressings by the combining of the PHEMA product with a water-miscible organic solvent such as polyethylene glycol, and optionally a plasticizer. A uniform set of physical properties of the PHEMA polymer particles is not apparent in the art on this subject. Variance of the physical properties depending upon the intended use of the wound dressing including the drug employed would appear to impact the physical properties of candidate PHEMA particles for use in the medical wound dressing art.